1. Field of the Invention
The present invention generally relates to a control apparatus for a throttle valve of an automobile engine. More specifically, the invention is directed to a control apparatus for controlling a relative opening degree of a pair of throttle valves rotatably mounted.
2. Description of the Related Art
In recent years, as means for controlling the engine to improve the exhaust emission controlling performance and fuel consumption performance, there has been developed a throttle valve controlling apparatus using an electrically controlled actuator in which a throttle valve and an accelerating pedal are not mechanically coupled, but the opening and closing of the throttle valve are controlled based upon a control signal. This control signal is obtained by converting an accelerating pedal operating amount into an electric signal (this signal is referred to as "an accelerator pedal operating amount signal") and signals indicative of the other engine operating state or vehicle running state (for example, these signals include an engine revolution speed signal, a gear position signal, and the like).
The throttle valve is opened and closed by a throttle valve drive motor. This motor operates in accordance with a command which is input from a vehicle controlling apparatus consisting of a calculation/controlling unit to sequentially calculate the optimal opening degree in correspondence to the engine operating state or vehicle running state. Therefore, it is necessary to provide a fail-safe device to prevent the runaway of the vehicle even if the electrically controlled actuator including the drive motor is made inoperative during the running of the vehicle. As a conventional example having such a fail-safe device, there has been disclosed a specific construction in Japanese Patent Publication No. 58-25853 (1983). That is, an electromagnetic clutch is employed to disconnect a throttle valve shaft from the drive motor when the engine becomes uncontrollable, and a return spring to fully close the throttle valve when the electromagnetic clutch is in the inoperative mode, is attached to the throttle valve shaft. On the other hand, in Japanese Patent Disclosure (KOKAI) No. 61-215436, there has also been disclosed an apparatus in which the throttle valve shaft is mechanically rotated through a differential gear device in response to a control amount of the electrically controlled actuator or an operating amount of the accelerating pedal.
However, according to such conventional apparatuses, when the electrically controlled actuator is once made inoperative, there is another problem such that although the runaway of the vehicle can be prevented, the continuous driving of the vehicle cannot be maintained and the vehicle cannot be moved to a repair shop.
The present invention is made to solve such conventional problems and it is an object of the invention to provide a throttle valve controlling apparatus having the higher reliability, and the higher response characteristic.
Another object of the invention is to provide a throttle valve controlling apparatus of an engine which can be also utilized to a traction control such that the engine torque is reduced by decreasing an opening degree of a throttle valve when drive wheels slip at the start and acceleration of the vehicle, or to an apparatus such that an opening degree of the throttle valve is reduced upon gear change in order to prevent a shock which is caused in the gear changing operation of an automatic transmission.